Tubular sheaths or sleeves having solid or continuous longitudinal bands of film connected together by longitudinal bands of mesh or net and which can be used to make bags or sacks for packaging, are described in French application no. 84-11518 of applicant's assignee.
Such tubular sheaths have alternate narrow bands of film and wide bands of a mesh or net structure, and are made by using an apparatus like the apparatus described in French patent No. 7143207 and its certificate of addition, No. 7240691.
In particular, apparatus to make such tubular sheaths or sleeves has an extrusion nozzle with an annular gap between two concentric extrusion die members, and which opens into an extrusion annulus. There are several toothed wheels which orbit around the axis of the draw plate and are simultaneously driven about their own axes. These toothed wheels are so positioned that the teeth of the wheels perforate the wall of the tubular sheath leaving the extrusion annulus. The wheels are placed in the immediate vicinity of the extrusion annulus and each wheel is positively driven in controlled rotation around its own axis by pinion gearing in mesh with a toothed ring gear. The perforations made in the tubular sheath, by the teeth of the wheels, as the sheath is extruded, are enlarged by stretching the sheath over a shaper or expander located under the extrusion annulus and over which the perforated sheath is moved.
The wheels make diagonal or inclined rows of perforations with respect to the longitudinal axis of the extrusion nozzle, the perforations being enlarged as the sheath is stretched over the expander to make a net or mesh structure with meshes, for example, in the shape of diamonds, the long diagnols of which are essentially parallel with the axis of the extrusion die. To form in the tubular sheath the alternate strips or bands of net structure and solid film structure, several teeth are usually omitted from each of the wheels so that the wheels only perforate certain longitudinal zones of the sheath as it is extruded. The perforated regions which form the net bands are stretched more than the solid film bands as the sheath is stretched over the expander. This technique is satisfactory when it is desired to make tubular sheaths with solid film bands which are relatively narrow with respect to the bands of net or mesh structure.
In certain applications, as for example when the sheath is used for packaging, or to make sacks, it is desirable to have relatively wide film bands, particularily for product descriptions or advertising.